A multiplicity of interventional procedures are performed, e.g. radiological or cardiological interventions, in which vascular diseases are to be diagnosed or treated. These interventional methods are often accompanied by image-based monitoring. In this case, the image-based monitoring is frequently performed by an x-ray system, e.g. a C-arm angiography system. Using the x-ray images which are produced in this way it is possible to show the position of the instruments that are used for the intervention, wherein said instruments can comprise catheters, guide wires, stents and other instruments.
However, the disadvantage of using monoplanar x-ray systems or generating merely two-dimensional image recordings is that the position of the relevant instruments can only be determined in two dimensions, i.e. in the plane of the image. Depth information which would allow three-dimensional positioning is not available.
The knowledge of the three-dimensional position of instruments is often advantageous, however, e.g. if there exists previously recorded three-dimensional image data by means of which the position of the instrument could be represented in three dimensions as a superimposition, for example. Such three-dimensional image data might exist as a result of e.g. magnetic resonance recordings, CT recordings or a previously performed angiography. If information relating to the three-dimensional position of instruments were available, navigation in the context of the intervention method would be simplified considerably.
Until now, there have been essentially two approaches which allow a three-dimensional localization of instruments.
These include firstly the so-called electromagnetic localization systems in which the position of the instrument is determined by means of a receiving coil, at the tip of the instrument, picking up signals from typically three transmitting coils which are located outside of the patient. By means of triangulation it is then possible to determine the three-dimensional position of the instrument.
In this type of configuration, however, it can be problematic that considerable additional hardware must be integrated into the system as a result of the transmission and reception electronics and the respective coils. In addition, the size of the receiving coils is not insignificant. Metal objects and the like can also cause interference in the electromagnetic field.
A further approach consists of three-dimensional localization using x-rays, in which at least two two-dimensional x-ray images are recorded from different directions, preferably simultaneously by means of a biplanar x-ray system. It is then possible to calculate a three-dimensional position of the instrument from the two-dimensional positions that can be derived from the images. In comparison with the electromagnetic method, this offers the advantage that any instruments can be used and that no further hardware is required apart from the x-ray system.
Using this approach, however, the problem exists that two x-ray images are necessary. This requires an expensive biplanar x-ray system. Alternatively, the two images can be recorded one after the other by changing the angulation of a C-arm. As a result of this, however, the refresh rate of the localization is significantly reduced in comparison with the typical image rate of approximately 15 images per second. The method can therefore no longer be used for the purpose of accompanying a navigation in real time.